Knowledge about the answers of onion production to different sources and quantities of biofertilizers as well as their effects chemical and microbiological attributes of the soil can provide important inputs to make the activity gainful and for soil fertility maintenance. In this sense, the objective of this work was to evaluate the agroeconomic viability of the onion production and the chemical and microbiological attributes of the soil in function to the application of biofertilizers. The experiment was conducted in the period from August to December of 2016, at the Fazenda Experimental Rafael Fernandes, located in Distrito de Lagoinha, Mossoró-RN. The experimental design used was in complete blocks randomized, in factorial scheme 2 x 5, with four repetitions. The first factor consisted of two sources of biofertilizers, worm humus based on cattle manure (Bio-HB) and goat (Bio-HC), and the second factor for five quantities of biofertilizers, that correspond to 50, 100, 150, 200 and 250% of fertilization with nitrogen recommended for the onion cultivation. The characteristics evaluated on the onion were: total productivity, commercial and non-commercial of bulb, commercial bulb classification, longitudinal and transverse diameter, bulb shape index, dry masses of the aerial part of the bulb and total, soluble solids, titratable acidity, relationship between soluble solids and titratable acidity, hydrogenation potential, bulb pungency and firmness, nitrogen, phosphorus, potassium, calcium and magnesium of the diagnostic leaf. The economic indices evaluated were: gross income, net income, rate of return and profitability index. The evaluated attributes of the soil were: levels of: P, K, Na, Ca, Mg, pH, MO, EC, sporulating bacteria, total bacteria, relations between sporulating and totals, actinomycetes, fungi and total microorganisms present in the soil after the harvest of the onion. The highest agroeconomic performance of the onion was obtained with the application of 100 and 250% of nitrogen with biofertilizers Bio-HC and Bio-HB, respectively. The applications of the biofertilizers fomented the increase in levels of the Mg, Ca and P of the soil, reflecting therefore, the improvement of soil fertility. At the highest proportions of nitrogen (200 and 250% N) Bio-HC was higher than Bio-HB in the amount of total microorganisms from soil. The system of organic cultivation of onion, in conditions of high soil fertility, is shown to be viable with the use of biofertilizers. However, it is necessary the conduction of further works on soils of lower fertility, to prove the efficiency of biofertilizers